1. Field of the Invention
The invention relates to the field of dynamic pressure sensors, particularly those employing piezoelectric elements.
2. Prior Art
Piezoelectric elements are known in the prior art and have been used in various transducers. Typically, these elements are polarized during fabrication and then cut in predetermined orientations for use in different modes of operation. Often transducers employ these piezoelectric element in either a bending mode, compression mode or shear mode. In the shear mode, one configuration which is utilized is sometimes referred to as the "bolted shear". In this configuration the piezoelectric elements are sandwiched between collector plates and bolted, along with these plates, to a support member. With this construction epoxy bonding is not required; moreover, this configuration is particularly insensitive to both acoustical excitation of the case and acceleration. Also with this "bolted shear" arrangement, the support member provides isolation from the strains in the base of the support member, and isolation from temperature gradients.
While in the prior art, piezoelectric elements operating in a shear mode have been employed in accelerometers, they have not been successfully employed in dynamic pressure sensors. The present invention employs the piezoelectric elements in a bolted arrangement, and thus obtains many of the advantages to this structure for a dynamic pressure sensor.
In U.S. Pat. No. 3,487,238 an accelerometer is disclosed which employs a piezoelectric element in a compression mode. This patent describes the manner in which the piezoelectric crystal may be fabricated and temperature compensation means which allows this accelerometer to successfully operate over a wide range of temperatures. As will be described in more detail in this application, the piezoelectric ceramic fabrication process of this patent may be employed to fabricate the piezoelectric elements used in the presently preferred embodiment.